1. Field of the Invention
The present invention relates to thermally-assisted magnetic recording heads that are mainly used for hard disk drive devices.
2. Description of the Related Art
Performance improvement of magnetic recording heads are demanded in conjunction with further condensing of recording density in hard disk drives (HDD). As magnetic recording heads, a composite-type magnetic recording head is widely utilized, the composite-type magnetic recording head having a structure in which a reproducing head including a magneto resistive effect element (MR element) for reading and a recording head including an induction-type electromagnetic transducer element for writing are laminated.
In magnetic recording, a magnetic recording medium, such as a magnetic disk and the like, is formed with an uncontinuous medium made from magnetic nanoparticles, and each magnetic nanoparticle has a single magnetic domain structure. Recording is performed using plurality of the nanoparticles. In order to increase recording density, unevenness of boundaries of recording regions should be reduced. In order to achieve that, the size of the magnetic nanoparticles should be decreased; however, the volume decrease of the magnetic nanoparticles accompanies the deterioration of thermal stability. A value that indicates thermal stability can be obtained by KuV/kBT. Herein, Ku is anisotropy energy of magnetic nanoparticles, V is the volume of one piece of the magnetic nanoparticles, kB is Boltzmann constant, and T is the absolute temperature. When the size of the magnetic nanoparticles is decreased, V is decreased and the value KuV/kBT that indicates thermal stability is decreased. Herein, it is considered that Ku may be increased to improve thermal stability; however, an increase of Ku accompanies an increase of coercive force. The size of a magnetic field generated by the magnetic recording head during recording is determined by saturation magnetic flux density of a nonmagnetic material of a core, and therefore coercive force of the magnetic recording medium is substantially limited.
As a method of resolving such thermal stability issue, a method of performing recording has been proposed. In the method, recording is performed while using a magnetic material having large Ku, applying simultaneously both a magnetic field and heat during recording, and decreasing coercive force. The method is called thermally-assisted magnetic recording. Thermally-assisted magnetic recording is similar to optical magnetic recording. However, in optical magnetic recording, spatial resolution depends on light; on the other hand, in thermally-assisted magnetic recording, spatial resolution depends on a magnetic field.
JP Laid-Open Patent Publication No. 2001-255254 discloses a technology of optical recording that uses a plasmon antenna that is configured with a metal scatterer and a film, the metal scatterer having a cone shape, a triangular shape, or the like formed on a substrate, the film made of a dielectric body or the like being formed around the scatterer. Also, JP Laid-Open Patent Publication No. 2003-114184 discloses a technology that generates further intense near-field light by letting a tip part of a plasmon antenna preferentially get close to a magnetic recording medium to concentrate charge. It has been known that, in the case of adopting such relevant technologies, conversion efficiency from propagation light incident from laser to near-field light is approximately 10%. Remaining energy of 90% may be reflected off an antenna surface, and may be absorbed by the antenna and be converted to thermally energy. Herein, the size of the plasmon antenna is set at the wavelength of light or less, so that the volume thereof becomes smaller and the temperature increase due to energy absorption of incident light becomes extremely larger. Due to such temperature increase, the problem that the plasmon antenna itself may melt occurs.
On the other hand, invented is a technology of coupling light to a metal via a buffer layer in a surface plasmon mode without directly irradiating the light to a plasmon antenna, the light propagating through a waveguide (U.S. Pat. No. 8,000,178). The above-described structure is called a surface plasmon wave-guiding-type antenna. Because such structure has a feature that the volume of a plasmon antenna is large, the structure has an advantage that the temperature increase of the antenna during performance of the antenna is small.
In a surface plasmon wave-guiding-type antenna, the temperature increase during performance is small compared to relevant technologies as disclosed in JP Laid-Open Patent Publication No. 2001-255254 and JP Laid-Open Patent Publication No. 2003-114184; however, drawbacks due to heat generation have not been completely resolved. For example, due to heat generation of the antenna, a diamond-like carbon (DLC) film formed on an air bearing surface (ABS) is evaporated. With further progression of heat generation of the antenna, corrosion of a magnetic pole and missing of a cladding layer may occur because the DLC film is evaporated. In order to prevent the occurrence of such problems to the extent possible, temperature of the antenna need to be set low to the extent possible.